Photomicrographs of sequential sections of skin biopsy from a patient with acute cutaneous GVHD: colocalization of CD34 staining, HA deposition, and lymphocyte adherence. (A,D) Immunohistochemical stain for CD34 antigen, demonstrating location of endothelial structures (original magnification × 20). (B) Adherence assay result, showing lymphocytes (dark blue dots) attaching to dermal papillary structure (methyl green-thionin stain, original magnification × 20). (C) Distribution of HA (original magnification × 20), histochemically identified using a biotinylated bovine HA-binding proteoglycan (bPG); skin sections treated with hyaluronidase (20 U/mL) before incubation with bPG revealed no staining, and incubation of bPG with soluble HA (0.3 mg/mL) before treatment of skin sections also prevented staining, confirming the specificity of bPG for the detection of HA (data not shown). Note the intense staining of HA in defined structures of papillary/upper reticular dermis (C) correlating with staining for vascular endothelial antigen CD34 (A,D) and with the location of adherent lymphocytes (B) within these sequential sections (A-D, arrows).